Two different obverse portraits were used for this coin and there
are three entirely different versions!

The obverse portrait of the Queen by Ian Rank-Broadley was used on all UK
coinage from 1998 to 2014 and also on some coins dated 2015 like this one.
The coin with the Ian Rank-Broadley portrait was only issued in 2015 Royal
Mint sets (and in some silver proof sets of 2015 coins).

The Royal Mint noticed that they had forgotten to mark the coin with a
denomination, but claimed that this was deliberate and perfectly fine as
the coin released later in 2015 for circulation would have the new Jody
Clark portrait of the Queen and would be marked with a denomination (in
other words – rectified).

At some stage between the first Ian Rank-Broadley coin and the final
circulation Jody Clark portrait coin with the denomination they seem to
have somehow produced silver and gold proof versions with an entirely
different obverse which has the Jody Clark portrait but also omits the
denomination!

with missing denomination can surely not be legal tender as the public can
hardly be expected to negotiate values of coins, even though that
obviously applies less to the silver and gold proof versions and the coins
are obviously 50p shaped! Was it a 50p, or is it, I wonder, a new larger
20p? Who knows.

they probably should have used obverse which shows both the
denomination and a date.